Therm-a-Rest Saros 20F/-6C Sleeping BagLightweight synthetic sleeping bag. If the forecast looks damp and your camp needs to be comfy, the Saros 32F 0C is the lightest bag in our Saros line of top rated synthetic sleeping bags. The Saros uses our eraLoft synthetic insulation, which is quick drying and weather resistant, making it ideal for backpacking and mountaineering in wet weather from spring to fall. The fit of the bag has been perfected in our onsite cold chamber to create our W. A.